DOC: use na_rep not nanRep in .to_csv()

nanRep works but is deprecated and emits a FutureWarning.
improve error message when xlrd import fails
DOC: cookbook/v0.11.1 updates
Merge branch 'from-records-fix-3682' of https://github.com/cpcloud/pandas into cpcloud-from-records-fix-3682

Conflicts:
	doc/source/v0.11.1.txt
BUG: inserting dups into blocks ok

CLN: finished duplicate item insert/delete - whoosh! (GH3679)

BUG: insert almost working

BUG: fixed insertion of dup columns!

ENH: added allow_duplicates kw to DataFrame.insert to indicate that inserting of

     a duplicate column should be allowed (default is False)
BUG: non-unique column index was failing in construction if from an ndarray

ENH: non-unique assignment now works

TST: more tests

BUG: handle multi-level columns correctly (original method)

CLN/BUG: raise exception if block ref_locs are not set when _set_ref_locs
BUG: not setting placement on reindex_with_indexers

ENH: extend index.reindex to handle non_unique indicies (rather than raising)

TST: more tests/optimizations for dup_columns
Merge pull request #3683 from jreback/dup_insert

BUG: allow insertion/deletion of columns in non-unique column DataFrames
Merge pull request #3700 from tdsmith/patch-1

DOC: use na_rep not nanRep in .to_csv()
DOC: document read_html and to_html

remove import of read_html
DOC: fix reference to read_html